Various processes for continuous casting of metal products are known in the art, but in comparison with casting of non-ferrous alloys, the continuous casting of steel is particularly difficult. The process used normally involves casting the steel in an open-ended mold with cooled walls limiting an inner tubular space, in which the product forms, the latter consisting of a liquid core surround by a skin consisting of a solidified surface shell. This product is discharged continuously through an orifice located at the exit of the mold, the latter usually having a vertical axis, and the product subsequently passes into a secondary cooling device, in which final solidification of the product takes place and which therefore has means of retaining and means of cooling the solidified faces of the product, the assembly as a whole being placed inside a frame forming a sort of tubular jacket surrounding the product, until solidification is completed.
To ensure continuity of casting, the metal, delivered in the molten state in a casting ladle, is poured into an intermediate vessel which makes it possible to ensure continuity of casting during the replacement of the ladle and which is itself provided with a casting hole, the discharge rate of which is adjusted in the conventional way by means of a spout and via which the metal is poured inside the mold. To prevent oxidation of the metal, a submerged nozzle is generally used, comprising a casting tube which penetrates the mold and which dips into the bath of liquid steel.
This process is now perfected as far as concerns the continuous casting of products of varied dimensions, in particular bars often called "billets" or sheets called "slabs". In this case, the inner tubular space of the mold has a rectangular shape limited by two wide walls and two narrow walls which correspond respectively to the long and short sides of the product. However, for casting under good conditions, and particularly to allow penetration of said nozzle into the mold, the slab must have a minimum width determining the thickness of the slab. To date, the minimal thickness of industrially cast slabs is approximately 150 mm.
The problem of the continuous casting of a thin product, i.e., a product of sufficiently small thickness to pass directly into a rolling mill, has been studied for a long time, even since the very start of research in continuous casting. However, the various processes heretofore proposed are generally based on new techniques, for example, wheel systems or cooled-strip systems, and have not yet been adopted for industrial use.
It has also been proposed to use these machines of the conventional type modified for the casting of thin strips.
For example, U.S. Pat. No. 2,564,723 proposes using a mold, the lower part of which has a flattened rectangular cross-section corresponding to that to be imparted to the product and the upper part of which is flared in the form of a funnel, so as to provide a widened central part making it possible to introduce the casting tube.
Such an arrangement solves the problem of introducing the casting tube, but does not make it possible to cast steel continuously on an industrial scale. In fact, after the filing date of the patent, it was found that, during casting, the mold had to be driven in vertical oscillation movements making it possible to prevent the solidified shell from adhering to the walls of the mold. The arrangement described in U.S. Pat. No. 2,564,723 does not allow such oscillating movements.
To solve this problem of oscillations, French Patent No. 1,505,630 also envisages a mold in the form of a funnel, but in which the wide walls converging downwards are composed of sectors of a cylindrical casing, allowing a circular oscillating movement. Such an arrangement is difficult to put into practice and, like the preceding one, assumes that the product is completely formed at the exit of the mold. Consequently, there is a risk of blockage as a result of a wedge effect, with pulling forces exerted in a particularly sensitive zone of the installation.